Highly-efficient and rapidly-fabricated dye-sensitized solar cells through molecular design of the Cu-complex hole-transport material

Abstract

Solid-state dye-sensitized solar cells (ssDSSCs) are promising for indoor energy harvesting, yet their fabrication and performance are limited by their coordination-complex hole-transport materials (HTMs). The effects of intermolecular packing and inner-sphere reorganization during redox both arise from the structural design of the coordination environment. Here, we show that ligand steric engineering provides a strategy to control these structural effects. By extending the 6,6′-substituents from methyl to butyl in a Cu(I)/Cu(II) diimine redox couple crystallization is inhibited, while coordination-sphere flexibility is also suppressed, leading to reduced geometric distortion upon oxidation. Thin-film diffraction and microscopy demonstrate the formation of amorphous, uniformly infiltrated networks under device-relevant conditions. This enables uniquely rapid and simple fabrication of efficient ssDSSCs, exhibiting power conversion efficiencies exceeding 10% under one-sun illumination and approximately 34% at 1000 lux under indoor illumination. These results establish steric control of intermolecular interactions as a transformative approach in coordination-complex HTMs and open up a new phase of ssDSSC development and application.